Cathode



March 12, 1957 G. LEWIN 2,785,332

CATHODE Filed June 27, 1952 ape/Wm 15M.

United States Patent CATHODE Gerhard Lewin, Maplewood, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 27, 1952, Serial No. 296,046

4 Claims. (Cl. 313-328) This invention relates to cathodes, and more particularly to one having utility with an ignitron.

While the cathode herein disclosed has utility in various electron discharge devices, arbitrary selection of a glow discharge ignitron has been made for illustration of one embodiment of preferred character. Use is made of the fact that a field arc can be instituted between a cathode and anode by first initiating a glow discharge therebetween. The heretofore unsolved problem has been to unfailingly obtain the transfer of glow discharge into the field arc. The primary object of the present invention is provision of a solution of this problem.

More specifically, the invention proposes a cathode having a surface capable of withstanding action of the cathode spot or field arc.

A further object of the invention is to provide field are promoting particles on the cathode surface and to retain such particles on the cathode surface and to retain such particles fixed in given position and distribution.

Other objects of the invention will appear to persons skilled in the art to which it appertains as the description proceeds, both by direct recitation thereof and by implication from the context.

The figure of the drawing is a vertical longitudinal section of an ignitron incorporating the cathode of my invention.

In said drawing, the reference numeral designates a cylindrical casing of steel or other sturdy material having a bottom 12 integral therewith and a top header 13 sealed at the upper rim of said casing to provide a closed envelope adapted to be evacuated. The header provides an appropriate lead-in seal 14 for an anode 15 supported in suspended position within the casing by a rod 11 from said seal. A sponge cathode 16 is held frictionally or otherwise on said bottom 12 of the casing, within the same, and in spaced relation to said anode 15. The sponge cathode is saturated with a reconstructing liquid cathode material such as mercury. Alkali metals and amalgams of alkali metals have also been found to function satisfactorily as the reconstructing liquid cathode material.

Ordinarily an ignitron utilizes a pool of mercury for the cathode, and has an ignitor dipping into the pool for creating a cathode spot and arc discharge at the desired moment. Some efforts have been made to eliminate the ignitor and obtain instead a glow discharge for supporting the field arc, but those efforts have not met with much success. It has been found that glow discharge can be promoted between a mercury pool and an anode in an ignitron by provision .of particles of insulating material 2,785,332 Patented Mar. 12, 19 57 ice planation of thus facilitating the transition to an are spot is that the particles become positively charged and produce the high field strength required to initiate a field arc. The particles, however, are not fixed in position, move around during handling and use of the ignitron, and are blasted away by the arc discharge and become lodged to a considerable extent on the anode and cause arc-backs. These defects have made such an ignitron impractical as a commercial device.

According to the present invention, I provide a sponge cathode body 16 wherein are included a comparatively even interspersed distribution of insulating arc initiating particles of which many are exposed at the upper surface of the cathode body toward the anode. The inclusion of these particles in the body of the sponge material, anchors them in place so they cannot move around nor be blasted away by the arc in use. Preferably said particles are sintered in place and that may be accomplished as part of the same sintering operation to which the body is subjected in normal formation of a sponge cathode. If preferred, the particles may be provided only at the upper surface of the sponge body. In any event, the particles preferably are substantially evenly interspersed at the exposed cathode surface. Silica particles prove to be very satisfactory for the purpose. Other examples of acceptable materials for the particles are alumina and thoria. I prefer that in plan view, the surface area of the sponge body shall not contain greater than 50% of the particle material and may well be considerably less, with a lower limit of about 5%.

The porous or sponge body material suited to this invention is molybdenum. I may also mention ruthenium as a very satisfactory material from operational standpoint, but at present its cost is prohibitive for commercial ignitrons. Iron is also usable although its erosion rate results in shorter life of the cathode. As to all of the mentioned materials, by sintering or other treatment, the same may be made into a porous body which will absorb mercury and present a surface wetted by the mercury as the cathode for the ignitron, and each is of a sufficiently refractory character to withstand the action of the cathode spot for considerable service hours.

While the foregoing examples of sponge materials satisfactory for use with glow-inciting particles are metallic and conductive, I may add that the sponge material may be insulative, but in that event, the flow-inciting particles incorporated therewith should be made of a different in-- sulative substance which will not be wetted by the mercury or other liquid cathode material used. If these particles are of a character that will be wetted by the mercury any of the herein mentioned particles must project sufliciently beyond the surface of the sponge to prevent said particles being completely covered by the mercury or the like, and in such a construction both the said body and the projecting particles may be of one kind of insulator material of adequately refractory characters.

I claim:

1. A cathode for ignitrons and the like comprising a body of insulative sponge material, and interspersed field arc-inciting particles anchored in said material.

2. A cathode for ignitrons and the like comprising a body of insulative sponge material, and interspersed insulative field arc inciting particles anchored in said material exposed at a surface thereof.

3. A cathode for ignitrons and the like in accordance with claim 1, wherein the exposed surface area of said sponge body contains said particles occupying from 5% to 50% of said exposed surface area.

4. A cathode for ignitrons and the like in accordance with claim 1, wherein both said body material and said particles are of one kind of refractory insulator material and said particles project in part from said sponge body to a height out of normal range of Wetting by mercury fed by capillarity through said body.

References Cited in the file of this patent UNITED STATES PATENTS Stoekle Dec. 28, 1926 Tonks Aug. 30, 1938 Smith Oct. 15, 1940 Depew Dec. 16, 1947 De Lany June 5, 1951 Lewin Nov. 4, 1952 Lewin Nov. 4, 1952 

